In the commercial production of rubber modified polyblends of the type wherein rubber particles of alkadiene rubber grafted with a styrene-type monomer and acrylonitrile-type monomer are generally uniformly dispersed in a matrix of a copolymer of styrene-type monomer and acrylonitrile-type monomer, which are commonly called ABS polyblends, it has heretofore been a common commercial practice to use either suspension or emulsion polymerization procedures for the preparation thereof. A given product resin is produced either as a result of a single batch polymerization or as a result of several batch polymerization followed by a physical blending procedure involving mixture of preformed graft copolymers with other graft copolymers or with ungrafted copolymer. Because of the inherent cost, complexity and sensitivity associated with such manufacturing technology, the art has recently been attempting to develop different techniques which would permit one to manufacture such resins using cheaper, less complex, highly reliable procedures and equipment. A particularly promising different technique would involve the use of mass polymerization which avoids such problems as product separation and recovery from the water used for suspension or emulsion polymerization.
To prepare ABS resins by all-mass polymerization technology has been heretofore proposed, but the practical realization of such a manufacturing route on a commercial scale is full of problems because of the difficulties of producing a product resin which is cheap enough to be competitive and still has the necessary and desirable physical properties for molding and extruding and for formed, manufactured product applications. Because of these difficulties, the art has combined some of the mass polymerization technology with some of the emulsion and/or suspension technology in an overall process.
U.S. Pat. No. 3,957,912 has disclosed such hybrid processes wherein the rubbers are grafted in aqueous emulsion as grafted crosslinked rubber particles and extracted from the aqueous phase by monomers into a monomer phase having said grafted rubber particles. The monomer phase is then separated from the aqueous phase and mass polymerized to an ABS polyblend.
Such polyblends generally have large amounts of grafted rubber particles present that range in size from about 0.01 to 0.5 microns based on the rubber particles as polymerized in emulsion. Rubber particles of this small size must be used in amounts of 15 to 45% in the polyblend to insure toughness, hence, lack rubber toughening efficiency. It has been found that small amounts of larger particles can be used in combination with the smaller particles to increase toughness without loss of gloss. Here, 5 to 50% of the large can be used to optimize toughness and chemical resistance wherein the large rubber particles have an average diameter of about 1 to 10 microns.
Large rubber particles, over about 0.5 microns, are difficult to prepare and graft in emulsion as such particles are not emulsion stable and the relatively small surface area does not provide for optimum levels of graft to insure their compatibility with the matrix copolymer phase.
It has been found that such large grafted rubber particles can be prepared by the mass polymerization of monomers having about 2 to 15% rubber dissolved therein as monomer-rubber solutions. During polymerization the rubber separates out as rubber particles having present about 1 to 5 parts of the monomers present as grafted and occluded polymers, said rubber particles having a particle size ranging from 1 to 10 microns. Such monomer-rubber solutions can be mass polymerized continuously to form ABS polyblend melts having about 2 to 15% of a rubber moiety which can be mixed and blended with the polyblend melts having rubber particles in the range of 0.01 to 0.5 microns as carried out in the present process.
U.S. Pat. No. 3,509,237 disclosed an ABS polyblend having grafted rubber particles with a bimodal particle size distribution. The process mixes an emulsion polymerized polymer with a suspension polymerized polymer, hence, does not provide the economics of using the mass polymerization process of the present process to prepare the final ABS polymeric polyblends wherein the matrix phase is all mass polymerized providing polymers of greater toughness and chemical resistance which have greater transparency and gloss.